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The cross-shaped concrete-filled steel tube (CFST) is a new shape of column, which avoids convex corners and increases the interior area of the room. Cross-shaped CFSTs possess high bearing capacity, good seismic performance and efficient construction speed. In this study, cross-shaped stub CFSTs under axial loading were tested. The key parameter is the width/thickness ratio of the cross-section. Experiments revealed that local buckling could be delayed and section capacity enhanced by reducing the tube width/thickness ratio. Moreover, a finite-element model was established using the commercial program Abaqus to simulate the compressive performance of the specimens. The results were used to confirm the precision of the finite-element model. Further, a parametric study was completed to inspect the effects of the tube width/thickness ratio, concrete strength and steel yield strength on the mechanical properties of specimens. Relying on the constitutive theoretical model of restrained concrete, an equation is recommended to calculate the section capacity of cross-shaped CFSTs. Finally, the practical outcomes and the calculated outcomes obtained from different design codes (AISC, AIJ, EC4, CECS and GB) were compared. The comparison results revealed that all recommended design codes underrate the section capacity of cross-shaped CFSTs. [ABSTRACT FROM AUTHOR]

• A new type of l -shaped steel–concrete composite shear wall using multi-partition steel tube was proposed. • The behavior under the eccentric load was investigated by the means of experiments and finite element analysis. • The proposed model using improved constitutional relationship of concrete simulated the eccentric behavior reasonably. • Simplified formulas were proposed to predict the N - M curves, which could consider the influence of load angle and slenderness. An l -shaped composite shear wall, comprised of a multi-partition steel tube and concrete, is developed to improve the behavior of the l -shaped component. It possesses high load-resisting strength and good ductility as it makes better use of steel and concrete. Eleven samples were tested under eccentric load to determine the impacts of the depth, breadth, and load angle. The experimental results showed that the eccentric strength of the specimen under a load angle π was higher than that of the specimen under a load angle of 0. The specimens failed in out-of-plane and in-plane flexural modes when the depth-to-width ratios were different. Then, the finite element (FE) model using an improved constitutional relation of concrete was established to analyze the eccentric mechanism of the l -shaped composite shear walls. Furthermore, parametric analysis using the FE model was taken to determine the key factors of eccentric behavior. Compared to the design methods specified in EC4, AISC, and CECS, it was found that the calculated capacity for the stub was underestimated while the calculated capacity of the slender components was overestimated. The simplified formulas were presented for predicting the N - M curves based on the experimental and FE analysis and it could conservatively include the influence of the load angle and the relative slenderness. [ABSTRACT FROM AUTHOR]

T-shaped welded multi-partition composite members, which are made of several rectangular concrete-filled steel tubes, are proposed to speed up the fabrication procedure. Seven half-scale T-shaped specimens were tested by considering the section height-to-width ratio and slenderness ratio. In the test, a slight torsion angle was measured when the instability failure along the asymmetric axis occurred, indicating the specimens had good torsion resistance. When the relative slenderness ratio of the specimen was larger than 0.44, the specimens failed due to the instability along the asymmetric axis. Parametric numerical analysis is conducted by considering the slenderness ratio, cross-section dimension, steel ratio, and material strength. The results show that the strength of concrete negatively impacts the ductility of the specimens, leading to a decrease of 43%, while the strength of the material positively influences the stability of the specimens. The formulas from different traditional codes are verified by the parametric numerical analysis results, indicating most codes can conservatively predict the sectional bearing capacity, but overestimate the stability coefficient of the specimens by neglecting the reduction effect of the excessive height-to-depth ratio. Recommendations are provided for calculating the stability coefficient under axial compression applicable to T-shaped welded multi-partition composite members. • Axial compression of T-shaped welded multi-partition composite members was studied through experiments and FE analysis. • The measured torsion angle confirms the good torsional capacity of T-shaped composite members. • Both sectional bearing capacity and stability bearing capacity have been discussed. • A suggestion for calculating stability coefficients is proposed, which is suitable for T-shaped columns and shear walls. [ABSTRACT FROM AUTHOR]

This study experimentally and numerically explores the axial-compression behaviours of tapered recycled aggregate concrete-filled high-strength double skin steel tubular (RAC-FHDST) stub column. Twelve specimens were fabricated and tested, considering the effects of tapered angle, hollow ratio and replacement level of coarse recycled aggregate (CRA). The experimental results, consisting of deformation patterns, axial load versus strain responses and confining effect from external high-strength steel tube were obtained and analyzed. Failure mode showed that all stub columns exhibited good ductile behaviour. The elastic stiffness and ultimate strength of RAC-FHDSTs decreased with rising tapered angles, while the ductile index increased. As the replacement levels of CRA varied from 0% to 100%, the elastic stiffness and ductility index obviously reduced. Larger confining effect from outer steel tube to RAC occurred close to the top section of specimens, and the occurrence of confinement was advanced with decreasing hollow ratio and increasing CRA content. Additionally, detailed numerical models were constructed and validated using experiment results. The validated finite element (FE) models were then employed to analyze the working mechanism of specimen, encompassing the load distributions and the interaction between the sandwiched RAC and steel tubes. Afterwards, a parametric study was performed to reveal the influences of essential parameters on the axial compressive performance. Finally, the existing design approaches to normal CFST and CFDST stub columns were employed to assess their applicability for estimating the ultimate strengths of tapered RAC-FHDSTs. • Axial-load tests conducted on 12 RAC-FHDST stub columns. • Effects of tapered angle, hollow ratio and CRA content on the axial response of RAC-FHDSTs. • Confinement effect from outer high-strength steel tube. • The applicability of existing design provisions to tapered RAC-FHDSTs. [ABSTRACT FROM AUTHOR]